1. Technical Field
The present invention relates to a drive circuit for switching elements which is applied to a power inverter circuit including a high-potential side switching element and a low-potential side switching element connected to the high-potential side switching element in series.
2. Related Art
This type of drive circuit is disclosed in Japanese Patent No. 3548497. The drive circuit detects the fact that an overcurrent is flowing to a semiconductor switching element (IGBT). In this drive circuit, the collector and the emitter of a switching element are connected to each other via a diode and a series connection of resistors. In particular, the anode of the diode is connected to one end of the series connection of resistors. The cathode of the diode is connected to the collector. In addition, the connecting point between the series connection of resistors and the anode of the diode is connected to the gate of the switching element via a resistor. The gate of the switching element is connected to an electronic power supply for charging the gate.
According to the above configuration, the fact can be detected that an overcurrent is flowing to the switching element, on the basis of the electric potential of the connecting point of the resistors connected in series. According to the principle of the detection, if the switching element is turned on, the gate is charged by the electronic power supply. Thereby, the gate voltage increases, and thereafter, the switching element is switched from an OFF state to an ON state.
When an overcurrent does not flow between the collector and the emitter of the switching element, the voltage between the collector and the emitter significantly decreases. Hence, a current flows from the gate to the collector via the diode. The electric potential of the connecting point between the series connection of resistors and the diode decreases. Hence, the electric potential of the connecting point of the resistors connected in series decreases to the electric potential in the vicinity of the electric potential of the emitter. In contrast, when an overcurrent flows, the voltage between the collector and the emitter is maintained at a high voltage even though the switching element is changed to an ON state. Hence, a current does not flow from the gate to the collector via the diode. Thereby, the electric potential of the connecting point of the resistors connected in series is a value obtained by dividing the gate voltage by using the resistors, and is higher than the electric potential in the vicinity of the electric potential of the emitter.
As described above, the fact can be detected that an overcurrent is flowing between the collector and the emitter of the switching element, on the basis of the electric potential of the connecting point varying depending on whether or not an overcurrent is flowing.
If an overcurrent is detected by the above technique, a configuration for transmitting information, which is concerning the fact that an overcurrent is flowing, to the outside of the present drive circuit is required, to appropriately perform a failsafe process later. In this case, to restrict the increase in the number of components and size of the drive circuit, the number of components of the configuration for transmitting information to the outside of the present drive circuit is required to be reduced.